T lymphocytes (i.e., T cells) play a key role in regulating immune responses in animals. Activation of T cells requires two signals delivered by antigen presenting cells to non-activated T cells. The first, or primary, signal is mediated by the interaction of the T cell receptor/CD3 complex (TcR/CD3) with MHC-associated antigenic peptide. The second, or costimulatory, signal regulates the T cell proliferative response and induction of effector functions. Costimulatory signals determine whether a T cell will be activated or inactivated to a state of tolerance. Molecules present on the surface of antigen presenting cells which are involved in T cell costimulation include B7 molecules. As known in the art, B7 molecules include two forms, B7-1 and B7-2, also known as CD80 and CD86, respectively. These molecules are counter-receptors for two ligands, CD28 and CTLA4. Both B7-1 and B7-2 bind both CD28 and CTLA4. Upon binding to CD28 or CTLA4, mouse B7 can cause T cells to proliferate and secrete interleukin-2 in conjunction with engagement of T cell receptor with a major histocompatability molecule complexed with peptide.
A full-length B7 protein is composed of several regions including, from the N-terminus, a signal peptide, an extracellular region, a transmembrane region, and a cytoplasmic region. The predicted amino acid sequence of B7-1 shares homology with members of the immunoglobulin (Ig) superfamily due to the presence of two contiguous Ig-like domains in the extracellular region. For example, in the mature mouse B7-1 protein, residues 1–112 share homology with the Ig variable (IgV) domain and residues 113–210 shares homology with Ig constant (IgC) domain (Freeman et al., J. Immunol., Vol. 143, pp. 2714–2722, 1989). B7-2 was also found to have similar structural features in the extracellular region. Similarly, CD28 and CTLA4 each have one IgV-like domain in the extracellular region.
Prior investigators have disclosed sequences encoding: human B7-1 domains are encoded by distinct exons in their respective genes as described for human B7-1 (Freeman et al., J. Immunol., vol. 143, pp. 2714–2722, 1989); human B7 (Azuma et al., Nature, vol. 366, pp. 76–79, 1993; or Selvakumar et al., Immunogenetics., vol. 36, pp. 175–181, 1992); rhesus monkey B7-1 (Villinger et al., J. Immunol., vol. 155, pp. 3946–3954, 1995); cat B7-1 (Hash et al., Thesis, Veterinary Pathobiology, Texas A & M, 1996); rabbit B7-1 (Isono et al., Immunogenetics., vol. 42, pp. 217–220, 1995); rat B7-1 (Judge et al., Intl. Immunol., vol. 7, pp. 171–178, 1995; Jackerott et al., Genbank Accession No. U10925, 1994); mouse B7-1 (Borriello et al., J. Immunol., vol. 153, pp. 5038–5048, 1994); human B7-2 (Freeman et al., Science, vol. 262, pp. 909–911, 1993); mouse B7-2 (Freeman et al., J. Expt. Med., vol. 178, pp. 2185–2192, 1993; or) and rat B7 genes (Judge et al., Intl. Immunol., vol. 7, pp. 171–178, 1995; Goodman, Genbank Accession No. U31330, 1995).
Prior investigators have also disclosed sequences encoding: mouse CTLA4 (Brunet et al., Nature, vol. 328, pp. 267–270, 1987); human CTLA4 (Dariavach et al., Eur J Immunol, vol 18, pp. 1901–1905, 1988); rabbit CTLA4 (Isono and Seto, Immunogenetics, vol. 42, pp. 217–220, 1995); rat CTLA4 (Oaks et al., Immunogenetics, vol. 43, pp. 173–174, 1996); and bovine CTLA4 (Parsons et al. Immunogenetics, vol. 43, pp. 388–391, 1996).
Messenger RNA of different sizes have been identified for B7-2 genes by Northern blot hybridization (Inobe et al., Biochem. Biophys. Res. Communic., vol. 200, pp. 443–449, 1994; or Boriello et al., J. Immunol, vol. 155, pp. 5490–5497, 1995). These B7-2 mRNA species have been assumed to be generated through alternative splicing or differential use of polyadenylation sites.
There remains a need for compounds and methods to regulate an immune response by manipulation of the function of B7-1 and/or B7-2.